Letter 35035

Can Zn/Co alloy plating withstand corrosion resistance [India] 

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Dear Sir,

We are leading manufacturers of automobile components. Now we are going to implement Zn/Co alloy plating on carbon steel-45C8(case hardened) material. Our query is

1) If the Zn/Co plated component can withstand corrosion resistance - Specification: No white rust within 250 hours and No red rust within 500 hours.

2)The above case hardened material alone(without plated) can withstand the above corrosion specification.

Kindly clarify.

N.V.SENTHILKUMAR
AUTOMOBILE COMPONENT MANUFACTURER - COIMBATORE, TAMILNADU , INDIA

Dear Mr Senthil Kumar,

Have no doubts, the coating that you specify does last the 500 hour Red Rust test; please ensure 10 microns.

Khozema Vahanwala Automaxx   Bangalore, Karnataka, India

You are looking for 250 hours to White rust. 500 hours to Red rust is easy, the white rust is more complicated.
The question is what kind of chromate do you intend to use.
A hex-chrome chromate will give you 250 hours to white rust BUT you cannot supply hex-chrome parts to the automobile industry.
The tri-chrome cannot guarantee 250 hours to white rust. You must use an organic sealer on top of it.

Sara Michaeli     chemical process supplier Israel

Dear S M;

You are dead right on your white rust observation; the spec Senthil is referring to is one of an Indian Motorcycle manufacturer which refers to hex chrome use.

Khozema Vahanwala Automaxx  Bangalore, Karnataka, India

Getting a good hexavalent passivate on zinc cobalt is difficult, and also zinc cobalt plating is just an expensive way of zinc plating. Salt spray results are not that different from standard zinc plating.

Chris Matthews
- East Sussex, England

Dear Mr Senthilkumar.
With reference to your query try zinc iron with tricromate will give clear 250 hr white rust. Also with hexa chrome you can achieve 250 plus white rust. Already Chennai based manufacturer marketing zinc iron alkaline medium process chemicals to meet your requirement;
Thanks.

P. Gurumoorthi     electroplating process chemicals Chennai, Tamilnadu, India

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